The use of a high-gradient magnetic field to separate magnetically attractable particles from a fluid in which they are suspended is well known. Moreover, magnetic separation devices are used in a variety of industries including pharmaceutical, medical, agricultural, scientific and engineering fields. For example in biotechnology, a high-gradient magnetic field may be used to separate magnetically labelled bone marrow cells from a blood sample.
WO 90/14891 DYNAL A.S. discloses a conventional magnetic separation device whereby a test-tube/sample vessel, containing a fluid in which magnetically labelled particles are suspended, is arranged adjacent a strong magnet. The labelled particles are magnetically attracted to the side of the test-tube nearest the magnet. Thus, the supernatant is easily removable from the test-tube using a pipette whilst the magnetically labelled particles are left in the tube.
In order to save time, it is often desirable to process a large number of samples at once using a linear rack-like arrangement or tray-like arrangement. For example, the magnetic separating device disclosed in WO 90/14891 DYNAL A.S. comprises a rack for supporting a plurality of specimen containers. At least one magnet is arranged adjacent the rear portion of each test-tube such that the magnetic particles are attracted and adhere to the inside surface of the test-tube nearest the magnet; i.e. the interior surface at the rear of the sample vessel.
In the separation protocols, it is often important that the particles are able to freely mix with the fluid prior to magnetic separation. It is therefore desirable for magnetic separation devices to be designed such that the portion that holds the sample is separable from the portion which houses the magnet. For such devices with separable portions, it is important that the portion holding the sample and portion housing the magnet are sufficiently fixed together during magnetic separation to provide efficient separation of the magnetic particles and fluid.
WO 2008/145712 Invitrogen Dynal A/S provides a magnetic separation device with a sample vessel retaining portion that is releasably mounted on the magnetising portion, with the sample vessel retaining portion configured as a female portion that receives the male magnetizing portion. In this arrangement a user needs to be careful when inverting the device during magnetic separation, to avoid any release of the sample vessel retaining portion from the magnetizing portion.
Commercial devices provide similar simple mechanical arrangements, for example the AXYGEN® IMAG™ MSD 12-tube magnetic separation device provides a male/female mounting arrangement to retain a top portion, which holds the sample tubes, in a magnetic base. A variant designed to work with 96 well microplates utilizes adjustable clips to hold the microplate in place, however this requires the user to manually adjust the clips to ensure that the microplate is retained the optimal separation occurs, adding to the complexity of the process. Incorrect adjustment of mechanical clips may result in non-optimal separation. In addition, mechanical clips are subject to wear, and worn clips may not operate effectively.
There is therefore a need for improved designs for magnetic separation devices that can alleviate and/or overcome at least some of the above-mentioned problems. More specifically, the invention seeks to provide a magnetic separation device with a sample holding portion that is releasably attached to the portion which houses the magnet in a manner which is more effective than the prior art. In particular, the invention seeks to provide a device with an releasable attachment mechanism that is easy to use and highly effective.